a. Field of the Invention
The present invention relates generally to apparatus and methods for obtaining measurements of human feet, and, more particularly, to an apparatus and method for obtaining measurements of the contours of human feet with the feet held in a preferred physical configuration, for use in the manufacture of orthotic devices or for other purposes.
b. Related Art
Obtaining accurate measurements of the human foot, and more particularly an accurate determination of its shape and contours, is desirable for many purposes. Perhaps the most basic reason is for the sizing and fitting of shoes, but beyond this are more particular purposes such as for constructing specialized shoe inserts and other orthotic devices. In general terms, the purpose of such orthotic devices is to optimize functions of the foot and/or to correct functional problems that result from deficiencies in the bone structure and/or associated soft tissues of the foot.
Although in many cases substantial benefits can be achieved using inserts and other orthotic devices constructed on the basis of one or more standardized or idealized models of feet, the characteristics of feet naturally vary from person to person, so that in general the maximum benefits can only be provided by a custom-fitted device. This is particularly true in the case of individual feet that differ significantly from the “norm” in terms of shape, structure and/or functional abnormalies. The construction of custom orthotics and similar devices in turn depends on obtaining an accurate representation of the person's foot and of the plantar (lower) surface of the foot in particular.
One traditional technique for obtaining a representation of a patient's foot has been to obtain a direct mold of the foot. For example, the foot may be placed in or covered with a material (e.g., plaster- or resin-laden cloth) that hardens to maintain its shape, in order to obtain a negative mold of the foot. The mold is subsequently filled with plaster or other hardenable material to form a positive representation of the foot, over which the orthotic device is then molded, with corrections being made to the shape of the cast as appropriate.
Although the traditional cast-molding system described in the preceding paragraph can yield excellent results, it is by nature highly labor intensive and time-consuming in practice; furthermore, the process of applying the material to the patient's foot and allowing it to take a set while holding the foot in position requires a minimum of several minutes to complete, during which the foot must be kept essentially immobile, causing inconvenience and potential discomfort to the patient as well as being fatiguing for the clinician. Moreover, common practice is for the molds of the patient's feet to be obtained by podiatrists and other practitioners in various locales and then sent to a specialist laboratory for actual manufacture of the orthotic devices, resulting in significant delays as well as shipping costs.
An alternative to forming a mold directly from the foot is to reduce the shape/contour of the foot to some form of data that can be transmitted to the laboratory for construction of the orthotic device. In some instances, this has been done by using one or more probes or other members that physically contact the foot at a series of locations to determine its contours; for example, certain devices have utilized an array of pin-like probes that are displaced when pressed against the plantar surface of the foot (or vice versa), with various distances by which individual pins/members are displaced representing the contours of the foot.
Other approaches have utilized optics in one manner or another; for example, some systems employ laser scanning mechanisms, with the location of points along the plantar surface of the foot being calculated from an angular relationship between the laser and or other sensor, while other systems project a pattern of lines or other geometric images onto the plantar surface from which the contours can be calculated; with currently available technology, a complete laser scan of the plantar surface of the foot requires only about fifteen seconds to complete, while digital imaging of the foot using projected lines requires a mere fraction of a second. The resulting data, typically digital, can then be conveniently transmitted to the laboratory for manufacture of orthotic devices, for example using a computer-controlled milling machine to form positive casts for molding of the orthotics, or even to form the orthotics themselves.
Systems that are able to produce digitized data accurately representing the contours of the foot, such as those noted above, offer significant advantages in terms of speed, efficiency, economy and patient comfort. However, despite these advantages such systems have on whole failed to provide entirely satisfactory results in terms of the end product, especially by comparison to the traditional molding process. One of the principal reasons, the inventor has found, is that in general such systems have necessarily imparted a degree of distortion to the foot during operation: For example, many prior optical scanners and imagers involve the patients standing on or otherwise placing their feet against a panel of glass or other transparent material, via which the plantar surfaces are exposed to the light source/sensor; pressing the foot against the panel causes the soft tissues of the foot to flatten and spread out in the areas of contact, so that when imaged the surface may be in a configuration that is far from optimal in terms of the function and comfort of the foot.
In addition to distortion of the soft tissues, a serious but somewhat more subtle problem relates to positioning of the bone structure of the foot. As is known to those skilled in the relevant art, the bone structure of the human foot transitions through a series of phases between heel strike and toe off, over what is referred to as the “gait cycle.” In particular the foot transitions from an adaptive phase at heel strike, in which the bone structure is comparatively yielding and is able to collapse somewhat to absorb impact and conform to the underlying surface, to a “rigid lever” phase, as weight begins to be transferred onto the forefoot, in which the bone structure becomes more-or-less locked so that the foot can provide stability and effective propulsion at toe off. The correct “locking” of the bone structure, and more particularly of the midtarsal joint, is critical for the foot to function properly, and is therefore a central goal of functional orthotic devices. Accurately configuring an orthotic device to meet this goal, however, requires being able to ascertain the contours of the foot with the bone structure in the correct end-point condition, specifically with the subtalar joint of the foot in what is referred to as the “neutral position” and with the midtarsal joint locked, which is generally difficult or even impossible to accomplish using prior systems such as those noted above. The matter is greatly complicated by the fact that individual feet vary greatly in terms of overall orientation (e.g., in the amount of pronation) when the joints of the foot are in the correct condition.
Accordingly, there exists a need for an apparatus and method for obtaining data representing contours of a foot, accurately and without distortion of the soft tissues or bone structure of the foot. Moreover, there exists a need for such an apparatus and method that is able to obtain the data representing the contours of the foot with the structure of the foot being held in the predetermined correct condition. Still further, there exists a need for such an apparatus and method that can be employed simply, efficiently and effectively in a clinical environment, and that in use is also convenient and comfortable for the patient.